Kidney dialysis is a medical procedure that is performed to aid or replace some of the kidney functions in severe renal failure. Hemodialysis, hemofiltration, hemodiafiltration, and peritoneal dialysis are all replacement therapies for patients who have lost most or all of their kidney function. Dialysis can remove many of the toxins and wastes that the natural kidney would remove in healthy patients. In addition, these therapies are used to balance the electrolyte or blood salt levels and to remove excess fluid that accumulates in patients with renal failure.
In addition to removing toxins and wastes from patients with kidney disease, excess fluid accumulated in patients suffering from renal failure is generally removed by the ultrafiltration action of a dialysis procedure. Removing fluid too slowly from a patient renders the fluid removal therapy inefficient, and may force the patient to undergo a longer procedure than necessary to remove the correct amount of fluid. If the treatment is ended with insufficient fluid removal, the patient can suffer from cardiovascular and pulmonary complications related to the resultant hypervolemia. Removing too much fluid from a patient, or removing fluid too quickly from a patient, can cause a dangerous loss of blood pressure.
Some methods for controlling the amount of fluid removed from a patient are known in the art. U.S. Ser. No. 13/864,913 describes a system using two tubes connected to a pump, wherein one tube delivers fresh dialysate into the system and removes fluid from a control bag into a drain, and the second tube removes fluid into a control bag. The change in weight in the control bag is therefore due to the net ultrafiltrate removed from the patient.
U.S. Pat. No. 8,202,241B2 teaches a blood purification system comprising multiple scales. A scale is provided for each storage container in the system. The net amount of fluid removed from a patient is therefore the sum of all of the changes in weight from each of the scales. The pump rates of the pumps attached to each of the storage containers can be changed if the net rate of fluid removed from the patient varies from some pre-set rate.
US20120085707A1 teaches a blood removal system with two pumps; one on either side of a dialyzer, and a dialysate reservoir on a scale. The two pumps are in communication with a control system. The output pump drives fluid from the dialyzer into a dialysate reservoir, while the input pump drives fluid from the dialysate reservoir to the dialyzer. The net amount of fluid removed from the patient is proportional to the change in the weight of the dialysate reservoir. If the change in the weight of the dialysate reservoir does not match the fluid removal prescription, then the pump rate of the output pump can be increased, or the pump rate of the input pump can be decreased.
The known dialysis systems outlined above balance fluid levels during therapy through gravimetric control, determining the net amount of fluid added or removed to the dialysate by the changes in the weights of various containers. These additional scales or control systems add to the size, weight and cost of the dialysis system. Other known methods for fluid balancing involve the use of coordination of the pumps that add fluid to the system and the pumps that remove fluid from the system. This requires highly accurate pumping means for each pump. These additional control systems necessarily add to the size, weight and cost of the dialysis system, and the highly accurate pumps add to the total cost of the dialysis system.
Some known systems control fluid movement across the dialysis membrane by means of balance chambers that coordinately pump equal volumes of fluid into and out of the dialysate ports of the dialyzer. The balance chambers comprise a fixed volume partitioned by a membrane or piston and, as fluid enters on one side of the partition, the partition is displaced by the incoming fluid and an equal amount of fluid is expelled on the other side of the partition. In balance chamber systems, net fluid removal from the patient across the dialysis membrane is accomplished by adding a fluid removal pump in fluid communication with the dialyzer outflow port and the outflow side of the of the balance chamber partition. In such systems operation of the fluid removal pump causes a greater amount of fluid to pass out of the dialyzer than into the dialyzer, resulting in net fluid removal from the patient across the dialysis membrane. In balance chamber systems the accuracy of patient fluid removal is dependent upon the accuracy of the fluid removal pump and other factors that can degrade the volumetric accuracy of the balance chambers such as fluid leaks within the balance chamber system and gas bubbles in the dialysate. Balance chambers can result in a pulsatile flow and if a smooth flow is desired, multiple sets of balance chambers are employed to reduce the pulsatility. Balance chambers can also increase the size and weight of a hemodialysis system as well as the total fluid volume required to operate the dialysate circuit and can be undesirable for hemodialysis systems that are small, portable and operate with a reduced amount of water.
Hence, there is a need for a system that can sense and balance the fluid levels during renal therapy. There is a need for a system that can selectively and accurately control the amount of fluid added to or removed from the patient during dialysis to ensure effective treatment and patient safety, without additional equipment that can add to the size and cost of the therapy system.